The present invention relates generally to detection of concealed or buried objects, and, more specifically, to detection of structural rebars inside concrete, and underground pipes for example.
At present, determining the condition of steel rebars inside reinforced structures like bridge decks, pavements, dams, and buildings is not practical. The rebars may be corroded, cracked, poorly welded together, wrongly spaced, or even missing. Lacking accurate, quantitative information on their location, it is impossible to realistically assess structural integrity and remaining service life. The knowledge of rebar condition would allow engineers to realistically prioritize repair and replacement activities, and detect and fix deterioration before more serious and expensive degradation occurs.
Similarly, at present it is very difficult, and in many cases not possible, to accurately locate and determine from the surface the condition of underground pipes for water, gas, and sewers. This is particularly true in cities, where numerous pipes often run under the same street. Many of these pipes have been seriously weakened by corrosion, or are leaking at their joints.
The ability to map underground pipes from the surface and pinpoint joints and local corrosion would be of great value to agencies and contractors by enabling repairs to be made quickly, with minimal disruption to traffic, and by preventing serious accidents or situations involving long periods without service.
Conventional techniques exist for magnetically locating underground pipes. For example, magnetic particles may be imbedded in pipes, or magnetic marking tapes may be buried with the pipe for allowing subsequent magnetic detection thereof using conventional magnetometers. In another prior art device, a transmitter is coupled to a known end of one or more underground pipes and generates different frequency signals therein which are picked up by a receiver at a remote location for locating the pipes. And, in a typical metal detector, a high frequency AC magnetic field is transmitted into the ground for being inductively coupled with a concealed metal object which in turn changes the resonance frequency to indicate location of the object.
Conventional detectors are limited in their ability to detect concealed objects. Furthermore, it is desirable to additionally determine the condition of the concealed objects to determine degradation thereof for example.